In a gearshift transmission, when shifting between a gear under load and a target gear, after the loaded gear has been disengaged a speed difference occurs at the transmission-internal gear clutch associated with the target gear and still disengaged, and this has to be equalized before the target gear is engaged, i.e. before the gear clutch concerned is engaged. This process is generally known as synchronization and takes place in practice by speed adaptation of the input-side part of the gear clutch which is in drive connection with the input shaft of the gearshift transmission.
During an upshift, after the loaded gear has been disengaged the input-side part of the gear clutch of the target gear rotates faster than the output-side part of the gear clutch, so that to synchronize the target gear the input shaft must be slowed down. In contrast, during a downshift, after the loaded gear has been disengaged the input-side part of the gear clutch of the target gear rotates more slowly than the output-side part or the gear clutch, so that to synchronize the target gear the input shaft must be speeded up.
In a gearshift transmission provided with synchronized gear clutches the synchronization of the target gear concerned or the gear clutch associated with that target gear is done by means of a friction-ring synchronizer device connected upstream from the actual gear clutch, which latter is provided with clutch tooth arrays that engage with one another by a positive interlock. During the synchronization of the target gear the speed difference at the gear clutch is equalized passively, i.e. by the action of the shifting force concerned, by virtue of frictional torque produced between the friction rings of the synchronizer device, before the gear clutch engages under the action of the shifting force so that the target gear can be engaged. Such lock-synchronized gear clutches, however, are of a relatively complex structure and are therefore relatively expensive to manufacture. Moreover, within the gearshift transmission, synchronized gear clutches take up a relatively large amount of space thus increasing the dimensions and weight of the gearshift transmission. Besides, since the way in which the synchronizer device works involves wear, the life of a gearshift transmission provided with synchronized gear clutches is necessarily limited.
In contrast to the above, unsynchronized gear clutches, which are generally referred to as claw clutches, are of simple and compact design, can be produced inexpensively, and during appropriately carried out shifts are little affected by wear so that they have a long life. However, in a manual transmission provided with unsynchronized gear clutches separate synchronization of the target gear concerned or the gear clutch associated with it is necessary. For the separate synchronization of the target gear it is known, for example, to slow down the input shaft of the manual transmission during an upshift by means of a transmission brake arranged on the input shaft or on a countershaft in driving connection therewith, and during a downshift to speed it up by partially engaging the separator clutch in combination with controlling the speed of the drive motor, which preferably consists of an internal combustion piston engine.
In such a case one begins with a transmission brake which cannot be adjusted but, by virtue of its design or by appropriate actuation with a constant contact force or a constant pressure, can be set to a constant braking torque MBr. The transmission brake and the associated actuating device can then have a simple, compact and inexpensive structure, which enables relatively simple integration into an existing manual transmission. However, the substantially constant braking torque MBr of the transmission brake may deviate from a nominal value due to external influences such as the ambient or operating temperature at the time and the wear condition of the friction linings, whereby the synchronization of the target gear in an upshift can be slowed down or speeded up. The separator clutch is an automated controllable friction clutch, which is used as the starting and shifting clutch, i.e. which is disengaged and engaged in a controlled manner for starting and shifting processes.
The arrangement of a transmission brake on the input shaft of a manual transmission made as a group transmission comprising a main transmission with a range group connected downstream from it is known, for example, from DE 10 2005 002 496 A1 (see FIG. 1 therein), in which the main transmission is designed as a multi-stage countershaft transmission and the range group as a two-stage planetary transmission. In contrast, the arrangement of a transmission brake on a countershaft in driving connection via an input gearwheel pair (input constant) with the input shaft in a manual transmission of countershaft design, is described in DE 102 42 823 A1 (see FIG. 3 therein).
In an upshift, to achieve rapid synchronization of the target gear and problem-free engagement of the unsynchronized gear clutch of the target gear, the braking action of the transmission brake, i.e. its braking torque MBr, should be as high as possible, the transmission brake should be engaged until the synchronous speed at the gear clutch concerned has nearly been reached, the transmission brake should be released when the gear clutch is engaged after an asymptotic approach of the input speed nGKE to the output speed nGKA, of the gear clutch of the target gear, and when the gear clutch is engaged, to assist the meshing of the clutch teeth there should still be a very small speed difference at the gear clutch. However, these requirements cannot be fulfilled solely by a transmission brake whose braking torque MBr is constant over the speed difference ΔnGK at the gear clutch which is to be reduced. Thus, at a high braking torque MBr the transmission brake can no longer be used below a certain speed difference ΔnGK, or the transmission brake may have such a low braking torque MBr that the synchronization of the target gear and hence the upshift process as a whole are greatly delayed.